1. Field of the Invention
This invention relates to pressure monitoring systems having an on-line transducer and a monitor for displaying operator readable output electronically derived from the on-line transducer, and more particularly to a method and apparatus for calibration verification of the on-line transducer with a known test pressure, and for selectively bypassing the on-line transducer in order to isolate defective electrical components of the pressure monitoring system.
The method and apparatus of the present invention has particular application to a system for direct monitoring of patient blood pressure and relates in part to subject matter disclosed in my copending U.S. patent application Ser. No. 654,373 for a PRESSURE TRANSDUCER filed on Sept. 25, 1984, and in copending U.S. patent application Ser. No. 608,761 for a DISPOSABLE PRESSURE TRANSDUCER APPARATUS FOR MEDICAL USE filed May 9, 1984, which are both incorporated herein by reference.
2. Background Art
The continuous monitoring of the pressure in a given environment is of importance in many aspects of manufacturing, transportation, health care, and energy production. Increasingly, pressure monitoring systems in these areas are of an electronic nature, utilizing a pressure transducer to convert the pressure in the environment monitored into an electrical signal reflective of the level thereof for display on a monitor.
For example, in medical science when monitoring direct patient blood pressure, it is known to couple a pressure transducer to a sterile fluid contained in a catheter inserted into a circulatory vessel of a patient. As the heart beats, the blood pressure waves are transmitted through the fluid in the catheter to the transducer, which produces an electrical output readable in digital or analog fashion on an electronic monitor. Advances in this area have produced miniature, yet sturdy, pressure transducers which are economical enough so as to be disposable after use with only a single individual patient.
With respect to pressure monitoring systems for use in this and other fields in which electronic pressure monitoring systems are significant, there is an important need to verify the accuracy of the monitoring system, both upon initial implacement and on a continuous basis during operation. The function of verifying an electronic pressure monitoring system involves two aspects.
First, the on-line pressure transducer of such a system must be tested through application thereto of a known test pressure to determine whether the transducer and its cooperating electronic equipment are functioning correctly together to read pressures monitored by the system. Calibration verification of the system against the known test pressure is thus one objective.
If, however, testing of the transducer and its cooperating electronic equipment reveals a malfunction in the monitoring system, a second aspect of verification requires that the source of the malfunction be isolated and then corrected. Typically, in order to accomplish this, electronic equipment has been required in addition to that used to check calibration of the on-line transducer. This additional electronic equipment simulates the electrical output behavior of the on-line transducer of the system and is connected to the system in place thereof, replacing it as the source of electrical signals to the monitoring system.
If this additional electronic equipment and procedure continues to reveal malfunctioning, then it can be assumed that the source of the malfunction resides, not in the on-line transducer, but in the electronic monitor or connecting cable of the monitoring system, although it is possible that both components and even the on-line transducer are each malfunctioning independently of the others. This knowledge then permits isolation of the defective electrical component, usually through interchanging one or the other of the monitor or cable used in the electronic system. On the other hand, if no malfunctioning of the electronic equipment of the system is manifested by this procedure, then the source of malfunction can be concluded to reside with the on-line transducer of the system. Understanding the location of any malfunction then permits its correction, usually by replacement of an appropriate component of the system.
Transducer simulators have in the past been devices which use complex resistive network circuitry to produce discrete levels of electronic signals imitating a transducer output through switching among an array of electronic components. These devices do not produce output signals within a continuous range of values, and in fact do not always reliably replicate the response of a transducer to a source of pressure within the range expected to be monitored.
Further, such transducer simulators, by not including transducers like those in place of which they are used, do not include the precise capacitive and inductive impedances thereof. They cannot, therefore, be expected to effectively simulate the interreaction of the transducer they replace with the monitor of the system being tested. This problem is only further compounded by the wide variety of monitors in use.